1. Field of the Invention
The present invention relates to a key mechanism, and more particularly, to a key mechanism in a computer keyboard.
2. Description of the Prior Art
Please refer to FIG. 1 an FIG 2. FIG. 1 is a schematic diagram of the key mechanism 11 of the prior art. FIG. 2 is a perspective view of the connecting device 17 of the key mechanism 11 shown in FIG. 1. The key mechanism 11 comprises a keycap 12, a base plate 14 set up below the keycap 12, a connecting device 17 connected between the keycap 12 and the base plate 14 for up-and-down movably installing the keycap 12 on the base plate 14, and a resilient element 19 installed under the keycap 12 for elastically supporting the keycap 12 in the upward direction and pressing downward on a pressure sensor (not shown) to generate a key-pressing signal. The connecting device 17 further comprises a first connecting piece 23 and a second connecting piece 24 pivotally connected to each other at their center portions 25 and 27 of the first connecting piece 23 and second connecting piece 24 respectively.
The first connecting piece 23 further comprises a front end 21 and a rear end 22 while the second connecting piece 24 comprises a front end 26 and a rear end 28. The center portion 15 at the front end 21 of the first connecting piece 23 is slidably connected to a corresponding guide channel 29 installed on the base plate 14 while the left and right sides of the rear end 22 are pivotally connected to the keycap 12. The left and right sides of the front end 26 of the second connecting piece 24 are slidably connected to the keycap 12 while the left and right sides of the rear end 28 are pivotally connected to the base plate 14. Therefore, in the key mechanism 11, the connecting device 17 uses a "three-point connection", making contact with the base plate 14 at three points: the center portion 15 at the front end 21 of the first connecting piece 23 as the first point, and the left and right sides of the rear end 28 of the second connecting piece 24 as the second and third points.
Please refer to FIG. 3 and FIG. 4. FIG. 3 is a schematic diagram of another key mechanism 10 of the prior art and FIG. 4 is a perspective view of the connecting device 16 of the key mechanism 10 shown in FIG. 3. Similar corresponding elements and component numbers are used in FIG. 3,4 as they are in FIG. 1,2. The main difference between the key mechanisms 10 and 11 is that the connecting device 16 shown in FIG. 3, 4 utilizes a four-point connection while the connecting device 17 in FIG. 1, 2 uses a three-point connection. As shown in FIG. 4, the connecting device 16 comprises a first connecting piece 18 and a second connecting piece 9. The left and right sides of the front end 20 of the first connecting piece 18 are slidably connected to guide channels 27 installed on the base plate 14. The left and right sides of a rear end 22 of the first connecting piece 18 are slidably connected to the keycap 12. The left and right sides of a front end 26 and a rear end 28 of the second connecting piece 9 are slidably and pivotably connected to the keycap 12 and base plate 14 respectively. Therefore, the connecting device 16 utilizes a "four-point connection" to connect to the base plate 14 by using the left and right sides of the front end 20 of the first connecting piece 18 as the first and second points and the left and right sides of the rear end 28 of the second connecting piece 9 as the third and fourth points.
Because of the continuing trend towards lighter and thinner keyboards, the internal components must also be made lighter and thinner. In order to meet these design requirements, the torsional strength of the first connecting pieces 23 and 18 is now relatively lower. These pieces are very susceptible to warping as they are the weakest elements in the entire key mechanism, especially when they are placed under an external force which is not in the center of keycap 12. This is especially true for long keys, such as the space bar.
There are two loading cases to be considered in the written description of the present invention. Loading case I is a balanced external force applied to the center of an element, or no force applied to the element. Loading case II is an unbalanced force applied to an element at an off-center point of the element.
Please refer to FIG. 5 and FIG. 6. FIG. 5 is the schematic diagram of warping under loading case II of the front end 21 of the first connecting piece 23 in the connecting device 17 shown in FIG. 1 and FIG. 2. FIG. 6 is a schematic diagram of warping under loading case II of the front end of the first connecting piece 18 in the connecting device 16 shown in FIG. 3 and FIG. 4.
As shown in FIG. 5, the central portion 15 will be deformed and bent downward, as indicated by the dotted lines, due to the constraints of the guide channel 29 and the base plate 14. As shown in FIG. 6, when the connecting device 16 is under loading case II, the central portion of the front end 20 of the connecting piece 18 will be deformed and bent upward, as shown by the dotted lines, due to the constraints of the guide channels 27 and lack of constraint at the central portion 39.
The warping of the first connecting pieces 23 and 18 will result in an unbalanced force being applied to the resilient element 19, and this unbalanced force will result in unstable key-press signals. Unstable key-press signals produce bad input, especially when a key is being held down.